Mercury boiler



0. L. WOOD v MERCURY BOILER July 7, 1942.

Filed May 28, 1941 2 Sheets-Sheet 1 6. 47 Attorneg.

July 7, 1942. o, woo 2,289,159

MERCURY BOILER Filed May 28, 1941 2 Sheets-Sheet 2 Inventof' Orla L.\X/ood I His Attorneg,

Patented July 7, 1942 MERCURY BOILER Orla L. Wood, Schenectady, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication May 28, 1941, Serial No. 395,537

15 Claims.

The present invention relates to mercury boilers and like elastic fluidgenerators in which a substantial portion of the heating tubes arelocated in a convection chamber above a drum with the upper ends ofthese tubes connected to receive heated mercury or like operating mediumfrom tubes located in a combustion chamber and the lower ends of thetubes connected to discharge a mixture of mercury liquid and vapor tosuch drum. The general arrangement of such a downward-flow convectionheating tube is disclosed and covered by the patent to Nerad, No.2,206,704, issued July 2, 1940, and assigned to the same assignee as thepresent application. This type of boiler may be operated with acomparatively small amount of operating fluid which during startingoperation fills only the tubes in the combustion chamber while the tubesin the convection chamber are empty during starting and receiveoperating fluid only as the mercury in the tubes subject to radiant heatin the combustion chamber expands and is expelled from such tubes.

The general object of my invention is to provide an improvedconstruction and arrangement of mercury boilers and like elastic fluidgenerators of the type above specified which may be operatedeconomically and. efliciently with a comparatively small amount ofoperating fluid.

A specific object of my invention is to provide an improved convectionheating tube arrange- 1 ment permitting a substantial increase of theconvection heating surface of a boiler.

Another specific object of my invention is to provide an improved tubearrangement in a combustion chamber whereby the walls of such cham- Kber may be substantially completely covered with a minimum number ofheating tubes requiring comparatively few and short headers forconducting liquid to the lower ends of such tubes.

For a consideration of further objects of my invention and of what Ibelieve to be novel and my invention, attention is directed to thefollowing description and the claim appended thereto in connection withthe accompanying drawings.

In the drawings, Fig. 1 illustrates a perspective View, partly brokenaway, of a mercury boiler embodying my invention; Fig. 2 is aperspective view of the boiler walls partly broken away; Fig. 3 is adetail View of a part of Fig. 1; Fig. 4 is a development of the tubecircuits and the walls of the boiler of Fig. 1, the tubes beingindicated in single, full lines, and the walls in dashdotted lines; Fig.5 is a single line diagram of the tube circuit, and Fig. 6 is anotherdetail View of Fig. 1.

The boiler, as illustrated in Fig. 2, is viewed from the rear out alonga vertical plane through the center of the boiler parallel to the sidewalls. The walls comprise a lower front wall Ill, an upper front wallll, a rear wall l2 and side walls [3 and M. The lower and upper frontwalls It and II are connected by an inclined roof IS. The lower endportions of the front and side walls are connected by a bottom whichincludes an inclined bottom wall l6 connecting the side walls and therear wall I2, 9. vertical bottom wall I! and a horizontal bottom wall I8connecting the side walls and the lower front wall It]. A horizontal,cylindrical drum 25) is supported on and secured to an opening 2| of theupper front wall H.

The lower portions of the side, front and rear walls below the roof l5form a combustion chamber 22 and the upper portions of the walls form aconvection chamber 23. Burners, not shown, for supplying fuel and air tomaintain combustion in the combustion chamber may be convenientlylocated inthe lower portions of the rear and front walls. The walls ofthe combustion chamber are completely lined with heating tubes. Inaccordance with my invention I provide four distinct sets of heatingtubes. These include a set of vertical tubes 24 lining the front wall itand the roof IS. The lower ends of these tubes are connected to a lowerheader 25 to which liquid is conducted from the drum 20 by a pluralityof downtube 26, 21 and 28. The downtube 26 is located in the cornerformed between the front wall It and the side wall l3. The lower portionof the tube 26 is reduced in diameter and connects to the end of thelower header 25. The other downtubes 21 and 28 conduct liquid from thedrum to intermediate portions of the lower header 25. The downtubes arelocated inside the furnace in vertical grooves or channels formed in thefurnace wall. These downtubes are protected from radiant heat by theuptubes.

A second set of heating tubes 29 lines the side wall l3. These tubes areinclined and, have inlet ends connected to receive mercury liquid fromthe aforementioned downtube 26. A number of the inclined tubes 29covering the upper portion of the side wall I3 in the combustion spacehave vertical intermediate portions 3i) and end portions 3| inclined ina direction opposite to the direction of inclination of the inletportions and connected to the drum 2E].

The tubes 29 include two lower end tubes 32 and 33, the first of whichhas a vertical portion 34 located behind the other tubes 29 and providedwith a plurality of studs or brackets 3411 (Fig. 6) for supporting theheating tubes 29. This support may be formed in any convenient manner,for instance, by a plurality of links connecting the vertical tube 34 tothe inclined tubes 29. The second of the two lower tubes 33 has avertical portion 35 located in the corner formed by the side wall I3 andthe rear wall l2 and acting as another support for the tubes 29.

A third set of tubes 36 has portions covering the inclined bottom wallIS. The inlet ends of the tubes 36 are connected to a header 3'! towhich operating liquid is conducted by a conduit 38 connecting theheader 3'! to the aforementioned header 25.

The two headers 25 and 31 and the connecting conduit 38 between them arelocated in the space formed between the vertical bottom wall I? and thelower portion of the front wall H). The connecting conduit 38 has aflexible intermediate portion 39 to avoid the setting up of stresses dueto relative expansion between the lower headers 25 and 31.

The third set of tubes 36 lining the bottom wall l6 has upper verticalportions 40 lining the central part of the rear wall l2. The verticalportions 48 are connected to the portions on the bottom wall by inclinedportions 4| (see Figs. 1 and 4).

A fourth set of heating tubes 42 is arranged to cover the side wall I4.These tubes are inclined and in all respects similar to the tubes liningthe other side wall |3. In particular, the tubes 42 have inlet endsconnected to a downtube 43 for receiving mercury liquid from the drum29. The downtube 43 for the tubes 42 corresponds to the downtube 26 forthe tubes 29. The tubes 42 are supported by two vertical tubes 44 and 45which rorm continuations of the two lowermost inclined tubes 42 andcorrespond to the tubes 34 and 35 on the wall l3. Some of the tubes 42near the upper portion of the combustion chamber are bent to formvertical portions 45 and oppositely inclined portions 41 connected tothe drum 2!]. Thus, the tubes 29 and 42 in the upper portion of thecombustion chamber line the side walls l9 and I4 respectively and haveends connected to the drum 28. The tubes 29 located in the lower portionof the combustion chamber are extended to form vertical tubes 48 liningthe left-hand portion of the rear wall l2. These vertical tubes 48 areconnected to the tubes 29 by inclined tubes 49 lining the rear wall [2adjacent the aforementioned inclined tubes 4|. The angle of inclinationof the portions 49, as best shown in Fig. 4, is the same as the angle ofinclination of the tubes 29. The tube portions 4| and 49 are so arrangedthat they cover substantially uniformly the lower portion of one-half ofthe rear wall l2.

The inclined tubes 42 covering the lower portion of the side wall M arelikewise extended to form inclined portions 58 and vertical portions 5|covering the right-hand half of the rear wall l2, as viewed in Fig. 2.

In order to reduce the amount of mercury liquid necessary for operatingthe boiler I provide in accordance with my invention a plurality ofvertically spaced banks of heating tubes in the con vection chamber 23.In the present instance I have indicated two banks of tubes, a bank 52(Fig. 1) located in the lower portion of the convection chamber and abank 53 located in the upper portion of the convection chamber. The

lower bank 52 comprises a plurality of horizontally spaced sets oftubes. Each set has a number of series-connected hairpin-shapedportions. The lower or outlet end of each set of the banks 52 and 53 isconnected to the drum 20. The upper ends of the sets of tubes of thelower bank 52 are connected to the upper ends of alternate tubes 48, 48and 5|. In the present instance I have shown two sets of tubes for thebank 52. The front set of the bank is connected to the first tube 45shown on the right-hand side of Fig. 1 and at the left-hand end of Fig.4. The second set of the bank 52 located behind the first set whenviewed in Fig. 1 is connected to the third tube 49. In other words, ifwe give the tubes 40 consecutive numbers, then the sets of tubes of thelower bank 52 are connected to the uneven numbers of the tubes 40. Thesets of tubes forming the bank 53 are connected to the even numbers ofthe tubes 40 and 48. Thus, the first set of tubes of the bank 53 isconnected to the second tube 48 from the right in Fig. 1 and from theleft in Fig. 4. The second set of tubes of the bank 53 is connected tothe 4th tube 48 from the right in Fig. l and from the left in Fig. 4. Inthis manner the upper ends of the tubes covering the rear wall l2 areconnected to the upper ends of the vertically spaced banks of tubes 52and 53. With the provision of two banks 52, 53 the even numbers of thetubes covering the rear wall l2 have upper ends connected to one bank oftubes and the uneven numbers have upper ends connected to the other bankof tubes.

During starting, as pointed out above, the boiler is filled with mercuryliquid to a point near the level of the drum, little mercury beingcontained within the drum. The banks of tubes located in the convectionspace are of considerable length. Therefore, during the startingoperation without the provision of further means it would takeconsiderable time until the mercury contained in the tubes in thecombustion chamber were forced through the banks 52, 53 and returned tothe drum and recirculated through the downtubes and the tubes in thecombustion chamber. Means are provided to effect circulation shortlyafter the starting period and thereby to eliminate the danger of theboiler running dry and of overheating certain riser and connectingtubes. These means in accordance with my invention include tubesconnecting a portion of the uptubes near the level of the drum to thedrum and other tubes for conducting mercury liquid to intermediatepoints of the banks 52 and 53.

More specifically, each tube for conducting liquid to the upper end of aset of tubes of the bank 53 has a lower end portion 54 (Figs. 1 and 3)alined with a corresponding end portion 55 of one of the tubes 48, 48and 5| and enclosed in a chamber 56. Each chamber 56 is connected by apipe 51 to a drain header 53 for conducting mercury liquid to the drum29. The chambers 56 are located slightly above the cold liquid level inthe drum 20. During starting, radiant heat transmitted to the mercury inthe combustion chamber causes expansion of the mercury liquid wherebysome of the liquid spills over from the end portions 55 into the chamber56 and is recirculated through the drain header 56 and the drum throughthe downtubes and the combustion heating tubes. During normal operationthe major portion of the liquid expelled from the tubes 55 is forcedinto the tube portions 54 and conducted to the upper ends of the sets oftubes of the bank 53. In

these tubes a substantial amount of the liquid is evaporated and themixture of vapor and liquicl is discharged from the lower ends of thetubes into the drum.

The second means for preventing overheating of the tubes in thecombustion chamber by increasing the circulation during the startingperiod comprise a plurality of tubes for conducting mercury liquid fromthe upper ends of the tubes 24 lining the front wall l and the roof l tointermediate portions of the sets of tubes of both banks 52, 53. Thus,as shown in Fig. 1, the tube 24 shown on the right-hand side has aportion 59 lining the roof I5 and forming an extension 60 connected toan intermediate point of the first or front set of tubes of the bank 52.The second tube from the right lining the front wall ID has an extension6| connected to an intermediate point of the first set of tubes of thebank 53. The third tube from the right lining the front wall Ill in Fig.l is connected to an intermediate point 62 of the second set of tubes ofthe bank 52 and the fourth tube 24 from the right in Fig. 1 is connectedto an intermediate point 63 of the second set of tubes of the upper bank53. In other words, with the tubes 24 consecutively numbered, the uneventubes 24 are connected to intermediate points of the set of tubes of thelower bank 52 and the even numbers of the tubes 24 are connected tointermediate points of the set of tubes of the upper bank 53. Conduitmeans 65 are connected to the drum for conducting mercury liquidthereto. Mercury vapor is discharged from the drum 20 through dischargeconduit 56.

The lower portion of the drum contains a known type of displacementblock Bl for displacing mercury liquid therein.

The heating tubes located in the combustion chamber are filled withmercury liquid to a level slightly above the connection of the drum 20with the mercury liquid supply conduit 65. During starting, the mercuryliquid contained in the heating tubes expands and as the liquid levelrises beyond the upper end portions 55 of the heating tubes 48, 48,which end portions are located at a level slightly above the cold liquidlevel in the drum, mercury liquid overflows the upper end portions 55,as explained above, and is passed through the connectors 57 and thedrain header 58 to the drum. With further rise in temperature themercury liquid contained in the inclined tubes 29 and 42 on the upperportions of the side walls I3 and I4, respectively, is forced throughthe outlet portions 3! and 41 of said tubes into the drum 2e, whence theliquid is recirculated. With increasing mercury temperature, furtherrecirculation through the drum takes place as soon as the mercury risesto the intermediate points of the lower bank 52 to which some of thetubes 2% are connected. With further increasing temperature, the mercuryreaches the upper ends of the tubes of the banks 52 and finally theintermediate points 63 of the upper bank 53 and, as normal operationtakes place, the mercury rises to the upper ends of the tubes of bank 53and is discharged therefrom to the drum. During normal operation amixture of mercury liquid and vapor is continuously discharged from alltube circuits into the drum 20. The mixture is separated in the drum,the liquid being recirculated through the downtubes and the vapordischarged through the discharge conduit66.

Thus, with the tube arrangement described above, mercury liquid is fedto the tubes in the convection chamber at various elevations, therebypreventing overheating of the tubes. Mercury is fed to those portions ofthe banks first which are located nearest the combustion chamber andmercury liquid is conducted to those banks or bank portions last whichare located farthest away from the combustion chamber and are subjectedto lower flue gas temperatures.

The combustion chamber described above is substantially rectangular incross section and has front and rear walls lined with substantiallyvertical tubes and side walls lined with inclined or sloping tubes. Thesloping side wall tubes have extensions turning onto and lining thefront wall or a part thereof. Another part of the front wall, in theabove example the central portion of the front wall, is lined with tubesconnected to or forming extensions of a row of tubes lining the bottomof the combustion chamher. With this arrangement it is possiblecompletely to line all of the walls with comparatively few tube circuitsand at the same time without requiring crossing of the tubes in theconvection chamber.

The entire boiler arrangement of drum, downpipes and uptubes ispreferably suspended from a supporting structure 68 near the lower endof the convection chamber 23, that is from thesame elevation near thetop of the boiler to permit relative expansion between the boiler casingand the tube system. This is especially true with regard to the supportof the sloping side wall tubes by vertical risers or cooled supportingtubes held near the top. The banks in the convection space, sometimescalled fog banks, may also be supported by cooled riser tubes on oneside and the discharge tubes from the upper bank or banks 53 on theother side of the bank 52 in. a manner similar to the arrangement shownin Fig. 6. The bank or banks 53 may be supported by compres-- sionspacers it? between the tubes, the bottom or discharge tubes ll of bank53 acting as the supporting columns.

The boiler requires only single comparatively short and direct downpipesto few lower interconnecting headers which also act as equalizers forthe circulating system and are arranged substantially vertically belowthe drum. The corner downpipes act as headers to feed the sloping sidewall tubes. In some instances, such as where the boiler is used forship-propelling purposes, the smallest variation in the lower headerpressure is insured, thus maintaining the pumping ability of the tubeswith the roll and pitch of a ship.

The tubes from the two lower headers line all of the Walls in thecombustion chamber. This is accomplished by having the upward slopingtubes covering the side walls turn the corner onto the front wall withthe same slope until they meet their lower adjacent tube. At. that pointthey turn vertically upward to cover completely the right-hand andleft-hand portions of the front wall. The tubes covering the floor orbottom bend up onto the front wall and cover the intermediate portionthereof. The entiretube arrangement in the combustion chamber actuallyincludes only three groups of tubes, one covering the rear wall andceiling, the other two covering the side Walls and the front wall. Thisreduces the number of tube circuits in the boiler, makes each circuitlonger and all circuits of substantially equal length, thereby effectingapproximately equal pick-up of radiant heat. The increased length ofeach circuit and the uniform and increased radiant heat pick-up producean increased pumping action suflicient to lift the mixture of liquid andvapor formed in the tubes of the combustion chamber a considerableheight above the normal level in the boiler drum to the upper ends ofthe banks of heating tubes in the convection chamber.

Substantially each tube in the combustion chamber passes along at leasttwo walls of the furnace, thereby insuring substantially uniform heatpick-up by the tubes.

What I claim as new and desire to secure by Letters Patent in the UnitedStates is:

1. A mercury boiler having walls forming a combustion chamber and aconvection chamber above the combustion chamber, a drum located at alevel near the lower end of the convection chamber, heating tubes liningthe walls in the combustion chamber, means including headers locatedsubstantially vertically below the drum for conducting mercury liquidfrom the drum to the lower ends of the heating tubes, and a plurality ofvertically spaced separate banks of tubes located in the convectionchamber and having upper ends separately connected to the tubes in thecombustion chamber to receive heated mercury therefrom and lower endsconnected to the drum.

2. A mercury boiler comprising walls having lower portions forming acombustion chamber and upper portions forming a convection chamber, adrum, uptubes lining the walls in the combustion chamber, meansincluding downtubes for conducting mercury from the drum to the lowerends of the uptubes, and a plurality of vertically spaced independentsets of tubes located in the convection chamber above the drum andhaving upper ends separately connected to separate uptubes and lowerends connected to the drum.

3. A mercury boiler comprising walls forming a combustion chamber and aconvection chamber above the combustion chamber, a plurality of heatingelements located in the combustion chamber, means for conducting mercuryliquid to the lower ends of the heating elements, a plurality ofvertically spaced independent banks of tubes located in the convectionchamber having upper ends separately connected to receive heated mercuryfrom the heating elements, and means connected to the lower ends of thebanks of tubes for receiving a mixture of mercury and vapor formedtherein.

4. A mercury boiler comprising walls forming a combustion chamber and aconvection chamber above the combustion chamber, heating tubes liningthe walls of the combustion chamber, means including a drum forsupplying mercury liquid to the lower ends of the heating tubes, a bankof heating elements located in the convection chamber above the level ofthe drum, means connecting the upper ends of the heating elements to theupper ends of some of the heating tubes, means connecting intermediatepoints of the heating elements to other heating tubes, and meansconnecting the lower ends of the heating elements to the drum.

5. A mercury boiler comprising walls having lower portions forming acombustion chamber and upper portions forming a convection chamber, adrum located near the lower end of the convection chamber, heating tubeslining the walls in the combustion chamber, means including downcomersfor conducting mercury liquid from the dim to the lower ends of theheating tubes, 9. bank of heating elements located in the convectionchamber having lower ends connected to discharge mercury into the drum,and separate means for connecting the upper ends and intermediateportions of the heating elements to the heating tubes.

6. A mercury boiler comprising walls having lower portions forming acombustion chamber and upper portions forming a convection chamber, adrum located at a level near the lower end of the convection chamber,heating tubes lining the walls in the combustion chamber, means forconducting mercury from the drum to the lower ends of the heating tubes,a plurality of vertically spaced banks of tubes located in theconvection chamber and having upper ends connected to separate heatingtubes in the combustion chamber and lower ends connected to the drum,and means for conducting heated mercury to intermediate points of atleast some of the banks of tubes.

'7. A mercury boiler comprising walls having lower portions forming acombustion chamber and upper portions forming a convection chamber, adrum located at a level near the lower end of the convection chamber,heating tubes lining the walls in the combustion chamber, means forconducting mercury from the drum to the lower ends of the heating tubes,a "bank of heating tubes located in the convection chamber, means forconnecting each heating tube of the bank to a heating tube in thecombustion chamber comprising connecting chambers located above the coldliquid level in the drum and sealed to spaced aligned portions of theheating tubes in the combustion chamber and the convection chamber toform an overflow for mercury discharged from the heating tubes in thecombustion chamber, and means including a drain header for conductinmercury from said connecting chambers to the drum.

8. A mercury boiler comprising walls having lower portions forming acombustion chamber and upper portions forming a convection chamber, adrum located at a level near the lower end of the convection chamber,heating tubes lining the walls in the combustion chamber, means forconducting mercury from the drum to the lower ends of the heating tubes,abank of heating tubes located in the convection chamber above the drumand having lower ends connected to discharge mercury into the drum,means for connecting the upper ends of the bank of heating tubes toseparate heating tubes in the combustion chamber, and means including adrain header communicating with the connecting means for conducting someof the mercury expelled from the heating tubes in the combustion chamberto the drum.

9. A mercury boiler comprising walls having lower portions forming acombustion chamber and upper portions forming a convection chamher, adrum located at a level near the lower end of the convection chamber,heating tubes lining the walls in the combustion chamber, means forconducting mercury from the drum to the lower ends of the heating tubes,a plurality of vertically spaced banks of heating tubes located in theconvection chamber with lower ends connected to discharge mercury intothe drum, some of the heating tubes in the combustion chamber havingupper ends directly connected to the drum, means for separatelyconnecting the upper ends of the other heating tubes to the upper endsand to intermediate points of the banks of tubes, the, last-named meansincluding connecting chambers forming overflow arrangements at a levelabove the cold liquid level in the drum with regard to mercury expelledfrom the upper ends of the heating tubes, and means including a drainheader for conducting mercury from the overflow arrangements to thedrum.

10. A mercury boiler having front, rear and side walls forming acombustion chamber, a drum located at a level near the upper end of thechamber, a plurality of sets of heating tubes lining the walls in thecombustion chamber and including a first set of vertical tubes liningthe front wall, second sets of inclined tubes lining the side walls, thesecond sets having extensions lining the rear wall, means for conductingmercury liquid from the drum to the heating tubes comprising a pluralityof downtubes having upper ends connected to the drum, and a lower headerconnecting the lower ends of the downtubes to the lower ends of thefirst set, two of the downtubes being located in the corners formedbetween the front and side walls and forming headers for the second setsof tubes.

11. A mercury boiler having front, rear and side walls and an inclinedbottom, a drum located above the combustion chamber, lower header meanslocated near the front wall substantially vertically below the drum,downcomers adjacent the front wall for conducting mercury liquid fromthe drum to the header means, two of the downcomers being located in thecorners formed between the front and side walls, and a plurality of setsof heating tubes lining the walls in the combustion chambers andincluding a first set of vertical heating tubes lining the front walland. connected to receive mercury from the header means, second sets ofinclined heating tubes lining the side Walls and connected to said twodowncomers, a third set of heating tubes lining the bottom and the rearwall, and conduit means for connecting the third set of heating tubes tosaid header means.

12. A mercury boiler having front, rear and side walls and an inclinedbottom, a drum located above the combustion chamber, lower header meanslocated near the front wall and substantially vertically below the drum,downcomers adjacent the front wall for conducting mercury liquid fromthe drum to the header means, two of the downcomers being located in thecorners formed between the front and side walls, and a plurality of setsof heating tubes lining the walls in the combustion chamber andincluding a first set of vertical heating tubes lining the front walland connected to receive mercury from the header means, second sets ofinclined heating tubes lining the side walls and connected to said twodowncomers, the second sets of heating tubes having extensions liningouter portions of the rear wall, a third set of heating tubes lining thebottom and having extensions lining the intermediate portion of the rearwall, and conduit means for conducting mercury liquid from the headermeans to the third set of heating tubes.

13. A mercury boiler comprising front, side and rear walls forming acombustion chamber, a drum located near the upper end of the chamber,heating tubes lining the walls in the chamber and including a set ofinclined tubes lining one of the side walls, means for conductingmercury liquid to the tubes including a downcomer located in the cornerformed between said side wall and the front wall, said downcomer beingconnected to said set of tubes, and means for supporting said set oftubes comprising a vertical tube forming an extension of one of the setof tubes and located behind the others of said set of tubes and aplurality of supporting members secured to said extension for engagingthe other tubes.

14. A mercury boiler having front, rear and side walls with lowerportions forming a combustion chamber and upper portions forming aconvection, the convection chamber having a cross-section smaller thanthat of the combustion chamber, an inclined roof connecting the lowerand upper portions of the front wall, an inclined bottom connecting therear wall and the side walls, means including an extension of the frontwall to form a channel below the combustion chamber, a horizontallydisposed cylindrical drum located above the roof, heating tubes liningthe walls in the chambers, means for conducting mercury to the lowerends of the tubes comprising a header disposed in the channel and aplurality of downtubes adjacent the front walls and connecting theheaders to the drum, and banks of tubes disposed in the convectionchamber and connected to receive heated mercury from the heating tubesand discharge it into the drum.

15. A mercury boiler comprising walls forming a heating chamber, a drumlocated at a level between the lower and upper levels of the chamber, aplurality of heating tubes having lower and upper portions disposedwithin the lower and upper parts of the heating chamber with the upperportions connected to discharge heated mercury to the drum and the lowerportions arranged to receive mercury liquid to be heated, connectingchambers between the lower and upper portions located at a level nearthe cold liquid level in the drum, and auxiliary tubes for conductingpart of the mercury discharged into the connecting chambers to the drumto assure circulation of mercury during starting of the boiler.

ORLA L. WOOD.

